An arsenic ion active DNAzyme includes a nucleotide sequence, which has a base sequence selected from ATCTCCTCCTGTTC (SEQ ID NO: 62), ATCTGCTCCTGTTC (SEQ ID NO: 63), ATCTCCTCATGTTC (SEQ ID NO: 64), ATCTCCTCTTGTTC (SEQ ID NO: 65), ATCTCCAACCTGTTC (SEQ ID NO: 66), and CCGTAGCGCAAAT (SEQ ID NO: 67). A mercury ion active DNAzyme includes a nucleotide sequence, which has a base sequence selected from AATTCCGTAGGTCCAGTG (SEQ ID NO: 68), AATTCCGTCGGTCCAGTG (SEQ ID NO: 69), AATTCCGCCGGTCCAGTG (SEQ ID NO: 70), GGTTCCGAGTCTCGCGTG (SEQ ID NO: 71), and CGTTCAAAAGGGGCACTG (SEQ ID NO: 72). Sensors incorporating the respective DNAzymes are also disclosed.